The present invention generally relates to a compressor, and more particular to a compressor having a gas passage structure capable of preventing a lubricating oil for lubricating a compression mechanism unit, which mixes into a high-pressure gas compressed by the compression mechanism unit, from being discharged to the outside of a sealed case.
A compressor for use in, for example, a refrigerator or an air conditioner, has a sealed case to which a suction pipe and a discharge pipe are connected. The sealed case accommodates a compression mechanism unit for compressing a refrigerant, and a motor unit with a stator and a rotor for driving the compression mechanism unit.
A pressurized gas compressed by the compression mechanism unit is temporarily discharged to the sealed case from a discharge port and then guided to gas passages provided in the motor unit. At last, the gas is discharged to an external device from a discharge pipe connected to the sealed case.
On the other hand, an oil reservoir for receiving a lubricating oil for lubricating the compression mechanism unit is formed at an inner bottom portion of the sealed case. The lubricating oil is sucked up in accordance with an operation of the compression mechanism unit. Then, the lubricating oil lubricates the respective slidable elements within the compression mechanism unit and returns to the oil reservoir in a circulating manner.
There is a possibility, however, that part of the lubricating oil in the state of mist (fine particles), which has lubricated the compression mechanism unit, may mix in the pressurized gas, and it may be brought to the gas passages in the motor unit and discharged from the discharge pipe to the external device.
The gas passages in the motor unit comprise gaps between a radially outside portion of the stator and a radially inside portion of the sealed case, through-holes formed in a stator core, slot gap portions between slots of the stator core and coils, an air gap between a radially outside portion of the rotor and a radially inside portion of the stator, and gas holes penetrating a rotor core.
In the prior art, when the gas passages comprising such gaps are designed, no consideration has given to the mutual relationship among the gas passages. For example, the ratio of the total area of the slot gap portions to the entire area of the gas passages (i.e. the total area of slot gap portions/the entire area of gas passages) is about 0.1.
In addition, the area of the slot gap portion associated with each slot is very small, compared to the area of the discharge port for temporarily discharging the compressed high-pressure gas into the sealed case, and the ratio of the slot gap portion (i.e. the area of slot gap portion per slot/the area of discharge port) is about 0.1.
In the above structure, the amount of lubricating oil discharged to the outside from the compressor increases because the lubricating oil in the state of mist mixes into the gas passing through the slot gap portions. Consequently, a sufficient amount of lubricating oil in the oil reservoir cannot be maintained, and the respective slidable elements in the compression mechanism unit may be destroyed.
To solve this problem, Japanese Patent No. 1,468,483, for example, discloses that a high-pressure gas coming up through an air gap is made to impinge upon an upper coil end and a centrifugal separation action is positively utilized to separate oil mist from the high-pressure gas and to return the oil to the oil reservoir at the inner bottom region of the sealed case through a gap existing at the outer periphery of the stator.
In modern air conditioners, in order to save energy and enhance comfortableness, an inverter drive system capable of varying the number of rotations of compressors is dominantly adopted. In this type of apparatuses, the number of rotations for the main driving is kept low once the room temperature is stabilized, but it is increased when the amount of circulating gas increases at the time of, e.g. start-up of driving. As a result, the above-described oil recovery cycle is not ensured.
Specifically, the high-pressure discharged into the sealed case from the discharge port of the compression mechanism unit goes up not only through the air gap between the rotor and stator, but also through the gap between the radially outside portion of the stator and the radially inside portion of the sealed case. Thus, even an oil, which may fall through the latter gap, is blown up and discharged to the outside of the sealed case.
Besides, in the conventional motor unit, the number of slots of the stator is set at a multiple of 3, which is greater than 20 (e.g. 24 slots). If the space factor of coils inserted in the slots is increased to enhance efficiency, little space is left for gas passages in the slots. It is also difficult to increase the air gap because the performance of the motor unit needs to be maintained at a sufficient level.
The object of the present invention is to provide a compressor with high reliability, which can reduce as much as possible a leakage of lubricating oil to the outside of the compressor and can always maintain a predetermined amount of lubricating oil in an oil reservoir formed at an inner bottom region of a sealed case, thereby realizing stable oil supply.
The present invention provides a compressor wherein a sealed case to which a suction pipe and a discharge pipe are connected accommodates a compression mechanism unit and a motor unit having a stator and a rotor for driving the compression mechanism unit, gas passages for passing a gas discharged from the compression mechanism unit are formed in the motor unit, and a ratio of a total area of slot gap portions defined between slots of a stator core and coils in a stator of the motor unit to an entire area of the gas passages is set at 0.3 or more.
According to the present invention, a leakage of lubricating oil to the outside of the compressor can be reduced as much as possible, and a predetermined amount of lubricating oil can always be maintained in the oil reservoir formed at the inner bottom region of the sealed case.